Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve Cluster related hole traps with enhanced-field-emission - the source for long term annealing in hadron irradiated Si diodes -* I. Pintilie1,2, E. Fretwurst2 and G. Lindstroem2 1 National Institute of Materials Physics, Bucharest, P.O. Box MG-7, 76900, Romania 2Institute for Experimental Physics, Hamburg University, D-22761, Germany * Article submitted to APL Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve Materials MCz-Silicon wafers: <100>, n/P, 100 μm, 1090 cm, Nd = 3.96x1012 cm-3, CiS process (samples 8556-02-25 and 8556-05-35) EPI-Silicon wafers: <111>, n/P, 72 μm on 300 μm Cz-substrate, 169 cm, CiS process standard Oxidation (EPI-ST) (sample 8364-02-35), Nd = 2.66x1013 cm-3, diffusion oxygenated for 24 h/1100°C (EPI-DO) (sample 8364-05-36) Nd = 2.48x1013 cm-3 Irradiation: - 1MeV neutrons at Ljubljana; fluences of 5x1013 cm-2 - Co60- gamma irradiation at BNL (300 Mrad dose) Annealing : Isothermal treatments at 80 0C Investigation methods: - I-V, C-V - TSC Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

TSC results-for fully depleted diodes H(116K) was detected previously* H(152K) ~ was atributed so far to CiOi * M. Moll, H. Feick, E. Fretwurst, G. Lindstroem, Nucl. Instrum. Meth. Phys. Res. A 409, 194 (1998) Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

TSC results-for fully depleted diodes Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

TSC results-for fully depleted diodes Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

H(116K), H(140K) and H(152K)- hole traps with enhanced field emission Filling of traps at 5 K Filling of traps at 50 K Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

Point defects and cluster related defects All H(116K), H(140K) and H(152K) are cluster related defects Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

How much CiOi can overlap to H(152K) peak ? For Tfilling< 30K no CiOi can be filled  As long as the forward injection is performed at Tfill< 30K the magnitude of H(152K) peak is not affected by the CiOi defect Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

TSC spectra analysis for traps with enhanced field emission In general, the TSC signal resulting from a hole trap in the diode is given by: where Pt is the concentration of the filled traps, ep is the emission rate of holes, w the depleted width of the diode, A is the active area of the diode. This formalism is not suited for traps with enhanced electric-field-emission, it may lead to huge errors in evaluating the defect level position in the band gap An identification of the mechanism behind the enhanced-field-emission depends on how the experimental data fits when different potentials are accounted for the defect Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

Mechanisms leading to an enhanced-electric-field-emission Poole Frenkel effect is characteristics to coulombic wells – where the carrier climbs over a barrier lowered by the electric field – seen for electric fields 103 - 106 V/cm – gives a clear indication about the charge state of the defect pure tunneling – the carriers are tunneling the barrier at high energy – possible only for electric fields > 107 V/cm – gives no indication about the defect charge state phonon assisted tunneling – the carriers absorb thermal energy from the latice and then tunnel through the barrier at a higher energy – seen for electric fields 104 - 106 V/cm Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve Poole Frenkel effect V(r) = -q2/40r –qFrcos, Ei= V(rmax)=-q(qFcos/ 0r )1/2 For one dimensional PF effect =0 and epPF=ep0exp(-Ei/kT) For three dimensional PF effect 0<  < /2 and where, for F has to be considered the local electric field in the p+n diode: F(x) = if V>Vd F(x) = if V<Vd Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

TSC spectra analysis for traps with enhanced field emission For Coulombic wells the emission rate depends on the local electric field and the corresponding TSC peak should be calculated according to: Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

Results for the fit of TSC peaks with 3D-PF The 3D-PF effect formalism describes the experiments  The H(116K), H(140K) and H(152K) centers have acceptor levels in the lower part of the gap  The H(116K), H(140K) and H(152K) centers contribute with their full concentration as negative space charge to Neff0 in the initially n-type silicon diodes Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

The levels position in the bandgap The parameters for the zero field emission rates describing the experimental results are: Ei116K = Ev + 0.33eV (0.285eV*) and p116K =410-14 (410-15*)cm2 Ei140K = Ev + 0.36eV and p140K =2.510-15 cm2 Ei152K = Ev + 0.42eV (0.36eV*) and p152K =2.310-14 (210-15*) cm2 Ec Eg/2 Ev P0/+ VO-/0 V2-/0 CiOi+/0 H152K0/- H140K0/- H116K0/- * - aparent ionization energy and capture cross sections when no field dependence of emission rates is accounted Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

The impact of H(116K), H(140K) and H(152K) defects on Neff These defects are responsible for the long term annealing of Neff Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve

Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve Summary Three cluster related acceptors in the lower part of the gap have been detected by TSC experiments. Their zero field activation enthalpies resulted from modelling the TSC peaks with the 3D-Poole Frenkel model and taking into account the spatial distribution of the diode electric field. It is shown that these acceptors are responsible for the long term annealing of Neff in hadron irradiated silicon diodes. Ioana Pintilie, 11 th RD50 Workshop, 12-14 November 2007, Geneve